Thermoplastic fluoropolymers have a unique combination of properties, such as high thermal stability, chemical inertness and non-stick release properties. Therefore, they are used in a great variety of fields related to high-temperature, aggressive chemicals and release applications. However, fluoropolymers are expensive in comparison to many other polymers. Multilayer structures provide a suitable means of reducing the cost of articles fabricated of fluoropolymers in which they are combined with other polymers which, furthermore, contribute their own properties and advantages such as, for example, low density, elasticity, sealability, scratch resistance and the like. When producing multilayer structures containing fluoropolymers there is always a problem of achieving appropriate interlayer adhesion to the fluoropolymer layer. Many fluoropolymers are non-polar and have very low surface energy (non-wetting surface). Interlayer wetting can be achieved by melting the fluoropolymer; however, upon solidifying, layers of the resulting multilayer product can be easily separated (delaminated). In most cases, interlayer adhesion is insufficient unless the fluoropolymer is chemically functionalized or its surface is chemically modified by special treatment techniques, which are both costly and complex. If the objective is to produce a multilayer article with a very thin fluoropolymer layer, modification of the interlayer surface can become a very costly or even impossible operation. Chemically functionalized fluoropolymers are expensive, and they are designed for adhesion to particular polymers such as nylons, and not to polyolefins. Functionalized forms of materials based on many thermoplastic fluoropolymers, such as a perfluorinated copolymer of ethylene and propylene (FEP), a copolymer of tetrafluoroethylene and perfluoromethylvinylether (MFA) or a perfluoroalkoxy resin (PFA) are not commercially available at all.
U.S. Pat. No. 3,650,827 (Brown et al., Mar. 21, 1972) describes a cable having a central copper conductor coated with a polyethylene composition. The control cable is subjected to an irradiation dose of about 10 megarads. A thin layer of a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) is extruded over the coated cable. Following extrusion, high-energy electron, X-rays or ultraviolet light is used to induce crosslinking in the FEP sheath at a temperature above the glass transition temperature of the FEP.
U.S. Pat. No. 4,155,823 (Gotcher et al. May 22, 1979) relates to melt processable fluorocarbon polymer compositions that require a processing temperature above 200° C. and are rendered radiation cross-linkable by incorporating crosslinking agents into the fluorocarbon polymer. The fluorocarbon polymer is exposed to a dose of radiation sufficient to provide a satisfactory degree of crosslinking without degrading the fluorocarbon polymer.
U.S. Pat. No. 4,677,017 (DeAntonis, Jun. 30, 1987) is directed to a multilayered film and a process to coextrude a multilayered film. The coextruded film has at least one thermoplastic fluoropolymer layer and at least one thermoplastic polymer layer adjacent thereto. An adhesive of a modified polyolefin resides between each thermoplastic fluoropolymer layer and each thermoplastic polymeric layer.
U.S. Pat. No. 5,480,721 (Pozzoli et al., Jan. 2, 1996) relates to the adhesion of fluorinated polymers to non-fluorinated thermoplastic materials by the use of an adhesive middle layer that comprises a blend comprising a fluorinated and a non-fluorinated thermoplastic and an ionomer or blends of more ionomers comprising copolymers having reactive groups which can be salified or not.
U.S. Pat. No. 5,578,681 (Tabb, Nov. 26, 1996) provides curable elastomeric blends of fluoroelastomer and ethylene copolymer elastomer in which at least one of the fluoroelastomer and ethylene copolymer elastomer contain a cure site monomer.
U.S. Pat. No. 5,916,659 (Koerber et al., Jun. 29, 1999) relates to stratified composites containing polymers which do not readily adhere to each other under the influence of heat and pressure. In particular, this reference relates to laminar composites consisting of discrete layers of fluoropolymeric and non-fluoropolymeric materials, which possess improved peel adhesive properties through the novel use of a fibrous binder.
WO 98/05493 (Spohn, E. I. DuPont de Nemours and Company, International Publication Date of Feb. 12, 1998) provides a laminate comprising fluoropolymer and polyamide layers, which laminate can be formed in a single extrusion step, i.e., by coextrusion, wherein the fluoropolymer layer and the polyamide layer adhere to one another without the presence of an adhesive tie layer.